Fix Print Preview failure state and add test

chrome/test/data/webui/print_preview.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 GEN('#include "base/feature_list.h"');
 GEN('#include "chrome/common/chrome_features.h"');
 
 /**
  * Test fixture for print preview WebUI testing.
  * @constructor
@@ skipping 133 matching lines @@
    * @device - The device whose capabilities should be dispatched.
    */
   setCapabilities: function(device) {
     var capsSetEvent =
         new Event(print_preview.NativeLayer.EventType.CAPABILITIES_SET);
     capsSetEvent.settingsInfo = device;
     this.nativeLayer_.dispatchEvent(capsSetEvent);
   },
 
   /**
+   * Dispatch the SETTINGS_INVALID event. This call is NOT async and will
+   * happen in the same thread.
+   */
+  invalidSettings: function() {

[dpapad, 2017/04/28 17:13:30]

Nit: |invalidSettings| sounds more like a data variable name than a function
name. How about renaming to "simulateInvalidSettings", or
"dispathInvalidSettings".

[rbpotter, 2017/04/29 00:07:11]

Done.

+    var invalidSettingsEvent =
+        new Event(print_preview.NativeLayer.EventType.SETTINGS_INVALID);
+    this.nativeLayer_.dispatchEvent(invalidSettingsEvent);
+  },
+
+
+  /**
    * Even though animation duration and delay is set to zero, it is necessary to
    * wait until the animation has finished.
    */
   waitForAnimationToEnd: function(elementId) {
     // add a listener for the animation end event
     document.addEventListener('animationend', function f(e) {
       if (e.target.id == elementId) {
         document.removeEventListener(f, 'animationend');
         testDone();
       }
@@ skipping 1185 matching lines @@
   // increments by 1 for each startGetPreview call it makes. It should only
   // make one such call during initialization or there will be a race; see
   // crbug.com/666595
   expectEquals(printPreview.previewArea_.previewGenerator_.inFlightRequestId_,
     -1);
   this.setInitialSettings();
   expectEquals(printPreview.previewArea_.previewGenerator_.inFlightRequestId_,
     0);
   testDone();
 });
+
+// Test that invalid settings errors disable the print preview and display
+// an error and that the preview dialog can be recovered by selecting a
+// new destination.
+TEST_F('PrintPreviewWebUITest', 'TestInvalidSettingsError', function() {
+  // Setup
+  this.setInitialSettings();
+  this.setLocalDestinations();
+  expectEquals('ready', printPreview.uiState_);

[dpapad, 2017/04/28 17:13:30]

Is there a way to avoid referring to a private variable from this test? Tests
that assert on private variables tend to test a specific implementation instead
of the observed behavior of the code they are testing.

Maybe assert that something that is observable by the user on the DOM (some
button being enabled, some message being shown etc).

[rbpotter, 2017/04/29 00:07:11]

Done.

+
+  // There will be an error message in the preview area since the plugin is
+  // not running. However, it should not be the invalid settings error.
+  var previewAreaEl = $('preview-area');
+  var customMessageEl =
+      previewAreaEl.getElementsByClassName('preview-area-custom-message')[0];
+  expectEquals(false, customMessageEl.hidden);
+  var expectedMessageStart = 'The selected printer is not available or not ' +
+      'installed correctly.'
+  expectEquals(-1, customMessageEl.textContent.search(expectedMessageStart));
+
+  // Manually enable the print button to verify it is disabled.
+  var printHeader = $('print-header');
+  var printButton = printHeader.querySelector('button.print');
+  checkElementDisplayed(printButton, true);
+  printButton.disabled = false;
+  expectEquals(false, printButton.disabled);
+
+  // Report invalid settings error.
+  this.invalidSettings();
+
+  // Should be in an error state, print button disabled, invalid custom error
+  // message shown.
+  expectEquals('error', printPreview.uiState_);
+  expectEquals(false, customMessageEl.hidden);
+  expectEquals(true,
+               customMessageEl.textContent.search(expectedMessageStart) > -1);
+  expectEquals(true, printButton.disabled);
+
+  // Select a new destination
+  var barDestination;
+  var destinations = printPreview.destinationStore_.destinations();
+  for (var destination, i = 0; destination = destinations[i]; i++) {
+    if (destination.id == 'BarDevice') {
+      barDestination = destination;
+      break;
+    }
+  }
+  printPreview.destinationStore_.selectDestination(barDestination);
+
+  // Should now have recovered. Error message does not change and the button
+  // will not be re-enabled since the preview never actually loads.
+  expectEquals('ready', printPreview.uiState_);
+  testDone();
+});